1. Field of the Invention
The present invention relates to a power device, and more particularly, to a multi-chip package in which a transistor, which is a switching device, and a control-integrated circuit (IC) which is a driving device, are mounted together in a package, thereby requiring a high insulation withstand voltage between the switching device and the control IC, and to a manufacturing method therefor.
2. Description of the Related Art
In power devices, a smart power switching (SPS) product contains a control IC, which is a driving device, and a transistor, which is a switching device. In a packaging process for SPS power devices, two chips are mounted together on one chip pad. However, in this case, an insulation means between the two chips, i.e., a control IC chip and a transistor chip, comes to the front as an important problem. During a packaging process, a common method of insulating the SPS power device is to attach one chip by inserting a ceramic plate or epoxy mold compound plate between die adhesives or to use a liquid non-conductive adhesive.
FIGS. 1 through 3 are cross-sectional views for explaining a conventional insulation method between two chips when the two chips are mounted on a chip pad. FIG. 1 is a cross-sectional view of a power device in which a ceramic plate is inserted between die adhesives for one chip. Specifically, a transistor chip 11, which is a switching device, is attached on a chip pad 10 by a conductive adhesive 12. In addition, a control IC chip 16 is attached by inserting a ceramic plate 15 between die adhesives 13 and 14 to provide insulation from the chip pad 10. Reference numeral 17 in FIG. 1 denotes a mold line coated with an epoxy mold compound that is used as a molding means. However, the above process has some problems in that a ceramic plate is breakable and expensive, so the manufacturing cost increases, and the overall packaging process becomes more complicated since a process of inserting a ceramic plate must be additionally performed therein.
FIG. 2 is a cross-sectional view of a power device in which an EMC plate is inserted between die adhesives for one chip. Specifically, a transistor chip 21, which is a switching device, is attached on a chip pad 20 by a conductive adhesive 22. A control IC chip 26 is attached with the EMC plate 25 inserted between die adhesives 23 and 24 to provide insulation from the chip pad 20. Reference numeral 27 in FIG. 2 denotes a mold line coated with an EMC which is a molding means. In this case, the EMC plate is cheaper than a ceramic plate, but there still remains problems in that a process becomes complicated.
FIG. 3 is a cross-sectional view of a power device in which a liquid non-conductive adhesive is used as a die adhesive. Specifically, a transistor chip 31 is attached on a chip pad 30 by a conductive adhesive 32. A control IC chip 36 is attached by a liquid non-conductive adhesive 35 to provide insulation from the chip pad 30. Reference numeral 37 in FIG. 3 denotes a mold line coated with an EMC which is used as a molding means. However, when using the liquid non-conductive adhesive 35, some problems occur. The overall thickness of a liquid non-conductive adhesive is not completely uniform so that a chip tends to be slanted.
Furthermore, in the course of hardening a liquid non-conductive adhesive after the control IC chip 36 is attached, a void occurs in the liquid conductive adhesive, so that it is difficult to ensure the stable reliability of the products. In addition, the control IC chip 36 and the non-conductive adhesive 35 are not completely attached together so that there is a crevice at the adhesion boundary, which is called delamination. This degrades product reliability.
In addition to the above method, there is a packaging method wherein the two chips are vertically attached to each other. This method has been disclosed in U.S. Pat. No. 5,777,345 titled xe2x80x9cMulti-chip Integrated Circuit Packagexe2x80x9d (Patent date: Jul., 7, 1998), U.S. Pat. No. 4,697,095 titled xe2x80x9cChip-on-Chip Semiconductor Device Having Selectable Terminalxe2x80x9d (Patent date: Sep. 29, 1987), and U.S. Pat. No. 4,703,483 titled xe2x80x9cChip-on-Chip Type Integrated Circuit Devicexe2x80x9d (Patent date: Oct. 27, 1987).
To solve the above problems, it is a first object of the present invention to provide a power device having a multi-chip package structure which is capable of ensuring sufficient insulation between two chips mounted on a chip pad, simplifying a process, and miniaturizing the overall size of a package.
It is a second object of the invention to provide a manufacturing method for a power device having the multi-chip package structure.
To achieve the first object, the present invention provides a power device having a multi-chip package structure in which a transistor, which is a switching device, and a control IC chip, which is a driving device, are mounted together in a package through a first embodiment. The power device includes a lead frame having a chip pad, an inner lead and an outer lead, a transistor chip, which is a switching device, attached on the chip pad of the lead frame by a conductive adhesive, a control integrated circuit (IC) chip, which is a driving device, attached on the chip pad of the lead frame at the side of the transistor chip by an insulating adhesive tape, a first gold wire for connecting a bond pad of the transistor chip and a bond pad of the control integrated circuit chip, a second gold wire for connecting a bond pad of the transistor chip and a bond pad of the control integrated circuit chip with the inner lead of the lead frame, respectively, and a molding means for molding the chip pad of the lead frame, inner lead, control integrated circuit chip, and first and second gold wires. Preferably, the conductive adhesive is solder, and an insulation withstand voltage required by the transistor chip is in the range of 500-1,000 V.
The insulating adhesive tape is attached at a temperature that is lower than the melting point of the conductive adhesive It has a single layered structure composed of polyimide base thermosetting resin or polyimide base thermoplastic resin or a multi-layered structure such as a triple layered structure comprised of a first adhesive layer, an insulating layer, and a second adhesive layer. In this case, the first and second adhesive layers are preferably polyimide base thermosetting resin or polyimide thermoplastic resin. The thickness of the insulating layer is preferably dependent on the insulation withstand voltage of the transistor chip.
To achieve the first object, the present invention also provides a power device having a multi-chip package in which a transistor, which is a switching device, and a control integrated circuit, which is a driving device, are mounted together in a package, through second and third embodiments. The power device includes a lead frame including a chip pad, an inner lead and an outer lead, a transistor chip, which is a switching device, attached on the chip pad of the lead frame by a conductive adhesive, an insulating adhesive means which overlies the central portion of the transistor chip surface excluding a predetermined region around the perimeter of the transistor chip surface, a control integrated circuit (IC) chip, which is a driving device, attached on the insulating adhesive means, a first gold wire for connecting a bond pad of the transistor chip to a bond pad of the control integrated circuit chip, a second gold wire for connecting a bond pad of the transistor chip and a bond pad of the control integrated circuit chip to the inner lead of the lead frame to one another, respectively, and a molding means for molding the chip pad of the lead frame, inner lead, transistor chip, control integrated circuit chip, and first and second gold wires.
Preferably, the conductive adhesive is solder, and an insulation withstand voltage required by the transistor chip is in the range of 500-1,000 V. Preferably, the insulating adhesive means is an insulating adhesive tape having a single-layered or multilayered structure. The insulating adhesive tape of the single layered structure is polyimide base thermosetting resin or polyimide thermoplastic resin. The insulating adhesive tape of the multilayered structure is a triple layered structure comprised of a first adhesive layer, an insulating layer, and a second adhesive layer. Preferably, the insulating adhesive means is a liquid non-conductive adhesive. The predetermined region which is not overlaid with the insulating adhesive means is at least the distance required for performing wire bonding.
To achieve the second object, the invention provides a manufacturing method for a power device having a multi-chip structure through a first embodiment. The method includes the steps of attaching a transistor chip, which is a switching device, to a chip pad of a lead frame by solder, attaching an insulating adhesive tape on the chip pad of the lead frame at the side of the transistor chip, attaching a control integrated circuit chip, which is a driving device, on top of the insulating adhesive tape using heat and pressure, performing wire bonding on the transistor chip and control integrated circuit chip, and performing a molding process on the resulting material. Preferably, the control integrated circuit chip is attached on the insulating adhesive tape, the surface area of the insulating adhesive tape is larger than the surface area of the control integrated circuit chip so that the distance from the edge of the control integrated circuit chip to the edge of the insulating adhesive tape can be equal to or greater than 100 xcexcm.
To achieve the second object, the invention also provides a manufacturing method for a power device having a multi-chip structure through second and third embodiments. The method includes the steps of attaching a transistor chip, which is a switching device, to a chip pad of a lead frame by solder, which is a conductive adhesive, forming an insulating adhesive means on top of the transistor chip, attaching a control integrated circuit chip which is a driving device on top of the insulating adhesive means, performing wire bonding on the transistor chip and control integrated circuit chip, and performing a molding process on the resulting material. Preferably, the insulating adhesive means is an insulating adhesive tape or a liquid non-conductive adhesive. If a liquid non-conductive adhesive is used as a conductive adhesive means, after attaching the control integrated circuit chip, a curing process for hardening the liquid non-conductive adhesive is further performed.
According to the present invention, firstly, a packaging process can be further simplified in a power device having a multi-chip package structure in which a transistor, which is a switching device, requiring a high insulation withstand voltage and a control integrated circuit, which is a driving device, are mounted together in one package. Second, the overall size of a package can be miniaturized. Third, the manufacturing cost of the devices is lowered.